Microcontroller

I use a PIC16F84A from Microchip
to control the TID. The reason is simply that Eelke Visser provides
source code (GPL) for this chip which made the development easier.

Programming the PIC

If you want to save the costs for a starter kit you can easily build
your own programmer. I use the Classic Tait Programmer for which the
components cost only a few Euros.

Here is my programmer:

Development tools

I use PiKdev to develop the
application.
PiKdev supports the Tait programmer and can program the PIC16F84 and
many more.
The application runs under Linux with KDE. There is also an addon to
calculate delay loops, PiKloops.

Board to connect to TID

The PIC can be placed together with the 24C65 and a fixed voltage
regulator on a small board. This will fit behind the TID without
problems.
My schematic is based on the layout of G�bor Gr�tzl (fogy.zip).
With the transistors at the outputs it is not needed to switch
input/output for the B ports.

Software

The program shows a welcome message when the car is started and then
every 5min a message from the EEPROM as scroll text on the TID.
The texts in the EEPROM begin at addresses 0000, 0100 to 1F00 and can
be 256 characters long. If you use a 64kBit EEPROM then 32 texts are
possible. All texts must have a null byte at the end.
The archive contains a PHP script which can convert the texts to a
format that is readable by txt2ihex.

Display

Scroll texts

The 24C65 includes texts which are displayed as scroll texts on the
display.

Speed display

You can get the speed signal from SDV at the TID connector. This
can be used to display the speed with much more accuracy than on the
tachometer.

There are 32 impulses for every rotation of the wheel on SDV. If you
know the wheel circumference you can calculate the current speed.
The time to count the impulses is set to a value where the number of
impulses is equal to the speed in km/h.

T = (3.6 * U) / 32 (U: circumference, e.g.
1.8m)

Top speed

After every speed measurement the top speed is changed, if needed. It
is permanently stored in the PIC's internal EEPROM.